The present invention relates generally to pulsed power systems, and more specifically, the invention pertains to pulsed power systems requiring a high-voltage, high-repetition rate trigger requiring a pulse having a fast-risetime. The invention finds use in driving circuitry for a recirculating linear accelerator in particular, and generally in wideband electronics countermeasure systems, short pulsed radars, communications systems, and calibration systems.
The task of providing the high-voltage triggers for high-voltage, high-power gas switches operating at greater than kilohertz repetition rates has been problematical. Although gas spark gap switches such as that taught in U.S. Pat. No. 3,983,438 by Levatter et al. issued Sep. 28, 1976, are capable of very high-power operation, they are typically limited in achievable repetition-rate. Improvements in this art have recently exhibited recovery times in the range of 100 microseconds by using undervolting techniques and hydrogen gas insulation as taught by U.S. Pat. No. 4,912,369 to Moran et al. issued Mar. 27, 1990. While this represented a double order of magnitude improvement in switch repetition rates and had the advantage of not requiring gas flow, no adequate triggering device was known to exist which exhibits multiple pulse capability.
Switch recovery tests are typically performed in a two-pulse configuration, where the switch is triggered only once and then the voltage is reapplied to determine switch recovery, thus requiring only a single-shot, high voltage trigger. No single compact device capable of providing a high rep-rate trigger was known. Typically, the trigger source for a high-power rep-ratable switch must be able to produce few-nanosecond risetime pulses at greater than a kilohertz rate while maintaining an output voltage level sufficient to initiate a discharge within the switch medium (usually greater than 100 kilovolts). In the past, multiple "single-shot" trigger sources attached to the switch in parallel through isolation diodes were necessary to achieve these requirements simultaneously. Unfortunately, the isolation diodes can add undesirable inductance to the trigger circuitry causing degradation in the achievable trigger risetime. In addition, the use of multiple trigger sources adds to the overall size and complexity of the pulsed-power system. Another common approach is to use a pulse transformer to step-up the output voltage of a relatively low voltage pulser containing fast switches (spark gap, thyratron, or solid-state switches) to the required high voltage. Although high voltages can be achieved with this method, the pulse transformer will limit the achievable risetime to an unsatisfactory level. Additional "peaking" spark gaps can be added to the output of such systems to improve the risetime, but this requires additional triggering circuitry and, as a result, more complexity and size. Any system containing a conventional spark gap as the switching element will be limited in rep-rate.
Various combinations of components forming Marx generators have long been used to produce single-shot, high-voltage triggers. These include patents to Asline, U.S. Pat. No. 3,845,322 issued Oct. 29, 1974, Feser, U.S. Pat. No. 3,821,561 issued Jun. 28, 1974, Bishop, U.S. Pat. No. 3,501,646 filed Oct. 3, 1967 and Rodewald, U.S. Pat. No. 3,504,191 issued Mar. 31, 1970. While these achieve varying degrees of voltage amplification, they lack high rep-rate capability. Other devices, such as that taught by Davis, U.S. Pat. No. 4,494,011 issued Jan. 15, 1985, use triode amplifier tubes to achieve a high power, short risetime pulse, but are limited in voltage. Finally, devices using a pulse forming network and transformer are known in the art as taught by Ranon, U.S. Pat. No. 4,996,494 issued Feb. 26, 1991 to produce high voltage but is also essentially a single shot device. U.S. Pat. Nos. 3,845,322, 3,821,561, 3,501,646, 3,504,191 are hereby incorporated by reference.
Coaxial Marx generators are also known in the art. One such generator is P/N 50082 available from Veradyne Corporation located at 330 North Victory Blvd., Burbank, Calif. 91502. These coaxial Marx generators are compact and pressurized with air to increase the hold-off voltage of the Marx elements. They are essentially single-shot devices.